Support generic types in signature inspection

[rcarriga]

The code #2580 was taken from existing code that was intended for an older Python version which didn't take the typing module into account. This patch removes the check for type instance, to allow the typing types such as Literal, Union, etc.

As the signature is only manually created, I don't see an issue with the complete removal of the check. The alternative is to ensure it is from the typing module but I can't find an easy way to do this without using the private types.

[Zac-HD]

Thanks for pointing this out, and for the patch!

I'm going to ask for something a little more complicated, though: because type annotations aren't the only possible use of function argument annotations, we'll still need to check that the thing "is a type (semantically)". Fortunately we already have the helper function for that:

hypothesis/hypothesis-python/src/hypothesis/strategies/_internal/types.py

Lines 94 to 96 in 2c76de1

	def is_a_type(thing):
	"""Return True if thing is a type or a generic type like thing."""
	return isinstance(thing, type) or is_generic_type(thing) or is_a_new_type(thing)

You'll probably need to import it locally inside the function though, to avoid import cycles. And then finally, we'll want a test that given e.g. def f(a: 1): ..., we don't treat that annotation as a type.

[rcarriga]

Did not realise that is_a_type existed, that's perfect!

[Zac-HD]

Nice! Two minor issues below; but you're pretty much done 😁

Most of the test failures are because Lark just released a new version which turns out to break our integration; I'll be fixing that in #2639 tomorrow.